Project Summary Individual rare diseases affect 6 ? 8 % of the world population, which is limited compared to more common diseases. Thus, developing therapeutics for these conditions generates little interest from the pharmaceutical industry, resulting in a tremendous unmet medical need. However, development of therapies for rare diseases ? especially in the context of underlying genetic and molecular mechanisms -- represents an area of great interest for the NIH. Usher syndrome is a rare disease characterized by concurrent hearing and vision loss. The loss of both hearing and vision creates a major communication burden and affects all aspects of life including health, education, social activities and employment. The long-term goals of this project are to develop an effective treatment for vision loss in Usher using antisense therapy; and establish the clinical parameters and measurable endpoints that could be used to determine the time to treatment and measure the potential therapeutic effect of testing antisense oligonucleotides (ASO) in future clinical trials. Usher syndrome is associated with mutations in sixteen genes creating four distinct clinical types. Usher-related genes and proteins express multiple tissue-specific variants that change over time, which creates a barrier to therapeutic strategies using gene-replacement therapy. To overcome this, we targeted the human 216A mutation in the USH1C gene that causes Type 1C Usher in the Acadian population, with an ASO that modulates mutant RNA splicing. Using a well validated Usher 1C mouse model that contains this human 216A mutation, we demonstrated that ASO treatment improves splicing of the Ush1c-RNA transcript and shows appreciable and significant rescue of vision and hearing. Therefore, the first aim of this study is to identify and characterize an USH1C-ASO drug therapy molecule that most effectively targets the 216A mutation and treats vision loss. We will test USH1C-targeted ASOs with different sequences and chemistries for efficacy and tolerability in Ush1c mice and patients? cells. The second aim is to determine the most robust clinical endpoints and identify potential trial participants to guide a clinical trial. We have identified a cohort of 52 USH1C patients in the three participating clinical centers. The patients will be invited to enroll in a prospective natural history study where we will measure standard of care and novel retinal and visual parameters at 6-month intervals over a 2-year period. These tests will allow us to define the clinical parameters to determine the outcome of our future trial. Successful completion of the proposed studies, will identify a lead ASO-drug candidate, demonstrate its preclinical efficacy, determine measurable clinical outcomes to guide a first-in-man ASO-based treatment for vision loss in USH1C and identify a cohort of potential trial participants.